In the field of graphic arts, an image-forming system showing very high contrast (in particular, showing gamma of 10 or higher) photographic characteristics is required for improving the reproduction of continuous tone images or line images by dot images.
Hitherto, for the above-described purpose, a specific developer called "lith-developer" has been used. The lith-developer contains hydroquinone only as the developing agent and further contains a sulfite as a preservative for not hindering the infectious developing property thereof in the form of an addition product thereof with formaldehyde for greatly lowering (usually not higher than 0.1 mole/liter) the concentration of the free sulfite ion. Accordingly, the lith-developer has a very serious disadvantage that the lith-developer is very liable to be air-oxidized and thus cannot endure storage over 3 days.
In order to obtain high contrast photographic characteristics, there are processes of using hydrazine derivatives described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857, 4,243,739, etc. According to these processes, photographic characteristics having very high contrast and high sensitivity are obtained and further since a sulfite can be added to the developer at a high concentration, the stability of the developer with respect to air oxidation is greatly improved as compared with the lith-developer.
However, the above-described image-forming system using hydrazine derivatives gives very high sensitivity and contrast and at the same time causes an undesirable phenomenon called "black spot" by infectious development, which becomes a large problem in the photographic process of making printing plates. "Black spot" (sometimes called "black pepper") is a dark spot which occurs at non-developed portions between dot images. The black spot increases where light-sensitive materials are stored, in particular under high temperature and high humidity, and also frequently occurs due to a reduction in the concentration of a sulfite ion generally used as a preservative. This defect also occurs due to an increase of pH value caused by the fatigue of the developer with the passage of time, which results in greatly lowering the commercial value of the light-sensitive materials used in the photographic process for making printing plates. Accordingly, intensive research has been conducted towards eliminating the occurrence of the black spot, but improvements heretofore have been accompanied by a reduction in sensitivity and gamma (.gamma.). Hence, a system capable of improving the occurrence of the black spot while keeping high sensitivity and high contrast has been keenly desired.